Load and Resistance Factor Design and Analysis of Stepped Crane Columns in Industrial Buildings

Load and Resistance Factor Design (LRFD), generally known as Limit States Design (LSD) outside of the United States of America, is replacing working stress design (WSD) worldwide for good reason. Not only does it provide much more uniform reliability with load and resistance factors based on the statistical variation of the relevant variables but also, by implicitly eliminating unnecessary conservatism at the same time, it can effect economies as well. A major advantage of LRFD over working stress design is inherent in the fact that the ultimate limit states, those associated with failure of all or part of the structure, are checked against factored load combinations, which are chosen to have the required low probability of being exceeded. This means that both the second-order geometric effects, resulting from the deformation of the structure and the non-linear effects due to material behavior can be taken into account in a straightforward manner at the load levels associated with failure. The load deformation response can be determined to whatever load level is desired. Herein this level is taken as that approaching the formation of the first plastic hinge. In working stress design the response is assumed to be linearly elastic but is not established beyond the working load level. Second-order effects cannot be included directly. The differences in the two analyses are demonstrated by White and Hajjar who show responses for various types of analyses.